The present invention relates to a binary optic-corrected, wideband imaging system incorporating a binary optical element (BOE) which provides aspheric correction for aberrations introduced by spherical optical elements. If the BOE is fabricated after other system elements have been fabricated and tested, it can also provide some correction for fabrication and assembly errors. The BOE allows high resolution, wide field-of-view imaging in a system comprising spherical or flat surfaces.
In high-performance imaging it is desirable for a system to provide high-resolution capability, wide field-of-view (FOV), low f-number, zero obscuration, and wide waveband operation with inexpensive spherical surface elements. Conventional technology achieves such performance from optical systems by incorporating a large number of spherical surface elements and/or several elements having aspheric surfaces. Optical systems implemented with large numbers of relatively heavy spherical surface elements may be found to have distinct size and weight disadvantages.
The size and weight problem often requires the use of aspheric surfaces, However, unlike spherical surfaces which are relatively easy to produce using existing optical fabrication technologies, the fabrication of aspheric surface elements requires a labor intensive, iterative polish and test manufacturing process. Thus, the cost of producing aspheric surface elements often is prohibitive. Also, machining difficulties generally limit aspheres to sections of rotationally symmetric conic surfaces.
Binary optical elements (BOEs) have been substituted for conventional optical elements in prior inventions. For instance, U.S. Pat. No. 4,846,552 discusses that BOEs fabricated by a process disclosed therein can be used for a binary grating telescope. In the arrangement of U.S. Pat. No. 4,846,552, two BOEs are present in place of conventional elements. Both BOEs are of the two-level grating type and each have substantial optical power (finite focal lengths). The patentee shows an off-axis telescope and suggests that the telescope is directed for use in optical laser radar systems. While the arrangements of U.S. Pat. No. 4,846,552 is suitable for narrow band laser systems, it would not likely provide the desired performance in a broadband incoherent imaging system as the BOEs have optical power.
An achromatic imaging system is disclosed in U.S. Pat. No. 4,550,973. In the system of U.S. Pat. No. 4,550,973, a diffractive hologram is positioned as the primary element. In order to achieve a broad wavelength passband, two holographic optical elements are provided with a lens therebetween. The first holographic optical element has positive optical power and the second holographic element has a negative optical power in order to cancel chromatic aberration introduced by the first holographic element.